Method of Treating Citrus Plants to Reduce Bacterial Infections

ABSTRACT

A method of treating a citrus plant is provided to reduce the incidence of one or more insect-vectored bacterial infections such as citrus greening. The method comprises the step of applying a treatment composition one or more times to the plant, wherein the treatment composition comprises an effective amount of aluminum tris(O-ethyl phosphonate).

FIELD OF THE INVENTION

The present invention is directed to methods of improving citrus plantgrowth by reducing the incidence of insect-vectored bacterialinfections.

BACKGROUND OF THE INVENTION

Problems with insect-vectored bacterial diseases in plants such ascommercial crops are well known and documented. There is often a seriousproblem with yield loss due to the lack of effective disease preventionor control measures, particularly for new strains of infectiousdiseases.

According to the United State Department of Agriculture, citrusgreening, also called Huanglongbing or yellow dragon disease, is one ofthe more serious diseases of citrus. This bacterial disease is thoughtto have originated in China in the early 1900's. The disease isprimarily spread by two species of psyllid insects. One species, theAsian citrus psyllid, Diaphorina citri, has been present in Floridasince 1998. The bacteria itself is not harmful to humans but the diseasehas harmed trees in Asia, Africa, the Arabian Peninsula, and Brazil.There are three strains of the bacteria: an Asian version, an Africanversion, and a recently described American strain discovered in Brazil.

The Asian strain, Candidatus Liberibacter asiaticus, was found inFlorida in early September, 2005. As a result, citrus greening diseaseis becoming a major threat to the U.S. citrus industry. Other than treeremoval, there has been no known effective control once a tree isinfected and there has been no known cure for the disease. Infectedtrees may produce misshapen, unmarketable, bitter fruit. Citrus greeningreduces the quantity and quality of citrus fruits, eventually rendering

infected trees useless. In areas of the world affected by citrusgreening the average productive lifespan of citrus trees has droppedfrom 50 or more years to 15 or less. The trees in the orchards usuallydie 3-5 years after becoming infected and require removal andreplanting. An infected tree produces fruit that is unsuitable for saleas fresh fruit or for juice.

Citrus plants infected by the citrus greening bacteria may not showsymptoms for years following infection. Initial symptoms frequentlyinclude the appearance of yellow shoots on a tree. As the bacteria movewithin the tree, the entire canopy progressively develops a yellowcolor.

The most characteristic symptoms of citrus greening are a blotchy leafmottle and vein yellowing that develop on leaves attached to shoots,providing the overall yellow appearance. These foliar symptoms maysuperficially resemble a zinc deficiency although the green and yellowcontrast is not as vivid with greening as it is with zinc deficiency oranother disease, citrus variegated chlorosis. Leaves with citrusgreening have a mottled appearance that differs from nutrition-relatedmottling in that greening-induced mottling usually crosses leaf veins.Nutrition related mottles usually are found between or along leaf veinsand leaves may be small and upright.

Fruit from diseased trees are small, often misshapen, and typically somegreen color remains on ripened fruit. On Mandarin orange, fruit maydevelop an uneven ripening such that they appear half orange and halfyellow. This symptom is the origin of the common name “greening.” Yieldsare almost minimal, and any developed fruit is rendered worthless due tosmall size, poor color, and bad taste.

It would be desirable to develop an effective chemical treatment methodfor the reduction of the incidence of insect-vectored bacterialinfections such as citrus greening that stunt citrus plant developmentor kill plants. An effective chemical treatment would overcome theinadequacies of the known control measures and improve plant growth byproviding systemic treatment, inducing plant self-defense, andcontrolling secondary infections such as fungal infections.

SUMMARY OF THE INVENTION

A method of treating a citrus plant is provided to reduce the incidenceof one or more insect-vectored bacterial infections such as citrusgreening. The method comprises the step of applying a treatmentcomposition one or more times to the plant, wherein the treatmentcomposition comprises an effective amount of aluminum tris(O-ethylphosphonate), which is known in the art as a fungicide.

DETAILED DESCRIPTION OF THE INVENTION

Other than in the operating examples, or where otherwise indicated, allnumbers expressing quantities of ingredients, reaction conditions and soforth used in the specification and claims are to be understood as beingmodified in all instances by the term “about.” Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical values, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of 1 to 10 is intended to include all sub-ranges between andincluding the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

As used herein, unless otherwise expressly specified, all numbers suchas those expressing values, ranges, amounts or percentages may be readas if prefaced by the word “about”, even if the term does not expresslyappear. Any numerical range recited herein is intended to include allsub-ranges subsumed therein. Plural encompasses singular and vice versa;e. g., the singular forms “a,” “an,” and “the” include plural referentsunless expressly and unequivocally limited to one referent.

With respect to the present invention, the phrase “effective amount” asused herein is intended to refer to an amount of an ingredient used suchthat a noticeable reduction in effects caused by insect-vectoredbacterial infections is observed in plants treated using the method ofthe present invention, compared to plants that did not receivetreatment.

The treatment method of the present invention comprises the step ofapplying a treatment composition one or more times to a citrus plant.The treatment composition comprises an effective amount of aluminumtris(O-ethyl phosphonate). A suitable source of aluminum tris(O-ethylphosphonate) is available from Bayer CropScience as Aliette®.

The method of the present invention improves citrus plant growth byreducing the incidence of one or more insect-vectored bacterialinfections, for example, citrus greening. Though not intending to bebound by theory, it is believed that phosphorous (phosphonic) acid has adirect and possibly an indirect effect on pathogens. It inhibits themetabolic process of oxidative phosphorylation. In addition, someevidence suggests that phosphorous acid and derivatives thereofstimulate a plant's natural defense response against pathogen attack.The phosphonate ion is highly systemic and fairly stable in plants. Thefully systemic activity allows the treatment composition to be appliedas foliar sprays, trunk applications, and soil/root treatments.Moreover, because of its systemic activity, upon application to theplant the phosphonate ion will be present in the plant phloem, wherecitrus greening bacteria infect the plant.

The treatment composition used in the treatment method of the presentinvention may further comprise one or more safeners or fungicides.Examples of suitable safeners include potassium carbonate, hydratedlime, or diammonium phosphate. Fungicides may be any of those known inthe art; in particular, fungicides containing phosphorous acid and/orderivatives thereof. Examples of commercially available fungicides ofthis type include ProPhyt®, available from Helena Chemical Company,Phostrol®, available from NuFarm Americas, Inc., and Agri-Fos®,available from Agrichem Manufacturing Industries PTY.LTD.

The treatment composition may be applied to the plants in an amount of 2to 7 lb/acre (0.91 to 3.18 kg/acre). It is typically applied in anamount of 5 lb/acre (2.27 kg/acre). The treatment composition may beapplied using any of a variety of techniques, including combinationsthereof. For example, the treatment composition may be applied one ormore times to roots of plants during planting or transplanting, such asduring transplanting of established plants; i. e., plants having atleast two mature leaves. Application may be in-furrow and/or as a rootdip. The treatment composition may additionally or alternatively beapplied one or more times to foliage, trunks and/or roots of plantsduring plant growth. Methods of application include spraying, painting,and/or chemigation. In certain embodiments of the present invention, thetreatment composition is initially applied one or more times to roots ofplants during planting or transplanting in-furrow and/or as a root dip,and then subsequently applied one or more times to foliage, trunksand/or roots of plants during plant growth. In these scenarios, thetreatment composition may be the same or different for each application.

In certain embodiments of the present invention, the treatment methodmay further include the step of applying additional compositionsincluding one or more pesticides such as insecticides and/or fungicides.In particular, acibenzolar-S-methyl, phorate, aldicarb, chlorothalonil,acephate, tebuconazole, and/or neonicotinoids such as imidacloprid,thiacloprid, acetamiprid, clothianidin, nitenpyram, and thiamethoxam aresuitable for use as additional treatment compositions. Each of these isavailable commercially and may be used in the method of the presentinvention in amounts conventionally recommended for their intended use.

Each of the treatment compositions used in the method of the presentinvention may independently be provided as emulsifiable concentrates,suspension concentrates, directly sprayable or dilutable solutions,coatable pastes, dilute emulsions, wettable powders, soluble powders,dispersible powders, dusts, granules or capsules. In addition to thecomponents discussed above, they may each optionally include auxiliaryagents commonly used in agricultural treatment formulations and known tothose skilled in the art. Examples include wetting agents, dispersants,emulsifiers, penetrants, preservatives, antifreezes and evaporationinhibitors such as glycerol and ethylene or propylene glycol, sorbitol,sodium lactate, fillers, carriers, colorants including pigments and/ordyes, pH modifiers (buffers, acids, and bases), salts such as calcium,magnesium, ammonium, potassium, sodium, and/or iron chlorides,fertilizers such as ammonium sulfate and ammonium nitrate, urea, anddefoamers.

Suitable defoamers include all customary defoamers includingsilicone-based and those based upon perfluoroalkyl phosphinic andphosphonic acids, in particular silicone-based defoamers, such assilicone oils, for example.

Defoamers most commonly used are those from the group of linearpolydimethylsiloxanes having an average dynamic viscosity, measured at25° C., in the range from 1000 to 8000 mPas (mPas=millipascal−second),usually 1200 to 6000 mPas, and containing silica. Silica includespolysilicic acids, meta-silicic acid, ortho-silicic acid, silica gel,silicic acid gels, kieselguhr, precipitated SiO₂, and the like.

Defoamers from the group of linear polydimethylsiloxanes contain astheir chemical backbone a compound of the formulaHO—[Si(CH₃)₂—O—]_(n)—H, in which the end groups are modified, byetherification for example, or are attached to the groups —Si(CH₃)₃.Non-limiting examples of defoamers of this kind are RHODORSIL® Antifoam416 (Rhodia) and RHODORSIL® Antifoam 481 (Rhodia). Other suitabledefoamers are RHODORSIL® 1824, ANTIMUSSOL 4459-2 (Clariant), Defoamer V4459 (Clariant), SE Visk and AS EM SE 39 (Wacker). The silicone oils canalso be used in the form of emulsions.

Whereas particular embodiments of this invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details of the presentinvention may be made without departing from the invention as defined inthe appended claims.

1. A method of treating a citrus plant to reduce the incidence of one ormore insect-vectored bacterial infections, comprising the step ofapplying a treatment composition to the plant, wherein the treatmentcomposition comprises an effective amount of aluminum tris(O-ethylphosphonate).
 2. The method of claim 1, wherein the bacterial infectioncomprises citrus greening.
 3. The method of claim 1, wherein thetreatment composition further comprises one or more safeners and/orfungicides.
 4. The method of claim 3, wherein the treatment compositionfurther comprises one or more fungicides containing phosphorous acidand/or derivatives thereof.
 5. The method of claim 1, wherein thetreatment composition is applied in an amount of 5 lb/acre (2.27kg/acre).
 6. The method of claim 1, wherein the treatment composition isapplied one or more times to roots of plants during planting ortransplanting, in-furrow and/or as a root dip.
 7. The method of claim 1,wherein the treatment composition is applied one or more times tofoliage, trunks and/or roots of plants during plant growth.
 8. Themethod of claim 7, wherein the treatment composition is applied totrunks.
 9. The method of claim 7, wherein the treatment composition isapplied to the plants by spraying, painting, and/or chemigation.
 10. Themethod of claim 1, wherein the treatment composition is initiallyapplied one or more times to roots of plants during planting ortransplanting in-furrow and/or as a root dip, and then subsequentlyapplied one or more times to foliage, trunks and/or roots of plantsduring plant growth, wherein the treatment composition may be the sameor different for each application.